1 // Copyright 2013 the V8 project authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4
5 #include "src/hydrogen-representation-changes.h"
6
7 namespace v8 {
8 namespace internal {
9
InsertRepresentationChangeForUse(HValue * value,HValue * use_value,int use_index,Representation to)10 void HRepresentationChangesPhase::InsertRepresentationChangeForUse(
11 HValue* value, HValue* use_value, int use_index, Representation to) {
12 // Insert the representation change right before its use. For phi-uses we
13 // insert at the end of the corresponding predecessor.
14 HInstruction* next = NULL;
15 if (use_value->IsPhi()) {
16 next = use_value->block()->predecessors()->at(use_index)->end();
17 } else {
18 next = HInstruction::cast(use_value);
19 }
20 // For constants we try to make the representation change at compile
21 // time. When a representation change is not possible without loss of
22 // information we treat constants like normal instructions and insert the
23 // change instructions for them.
24 HInstruction* new_value = NULL;
25 bool is_truncating_to_smi = use_value->CheckFlag(HValue::kTruncatingToSmi);
26 bool is_truncating_to_int = use_value->CheckFlag(HValue::kTruncatingToInt32);
27 if (value->IsConstant()) {
28 HConstant* constant = HConstant::cast(value);
29 // Try to create a new copy of the constant with the new representation.
30 if (is_truncating_to_int && to.IsInteger32()) {
31 Maybe<HConstant*> res = constant->CopyToTruncatedInt32(graph()->zone());
32 if (res.has_value) new_value = res.value;
33 } else {
34 new_value = constant->CopyToRepresentation(to, graph()->zone());
35 }
36 }
37
38 if (new_value == NULL) {
39 new_value = new(graph()->zone()) HChange(
40 value, to, is_truncating_to_smi, is_truncating_to_int);
41 if (!use_value->operand_position(use_index).IsUnknown()) {
42 new_value->set_position(use_value->operand_position(use_index));
43 } else {
44 DCHECK(!FLAG_hydrogen_track_positions ||
45 !graph()->info()->IsOptimizing());
46 }
47 }
48
49 new_value->InsertBefore(next);
50 use_value->SetOperandAt(use_index, new_value);
51 }
52
53
IsNonDeoptingIntToSmiChange(HChange * change)54 static bool IsNonDeoptingIntToSmiChange(HChange* change) {
55 Representation from_rep = change->from();
56 Representation to_rep = change->to();
57 // Flags indicating Uint32 operations are set in a later Hydrogen phase.
58 DCHECK(!change->CheckFlag(HValue::kUint32));
59 return from_rep.IsInteger32() && to_rep.IsSmi() && SmiValuesAre32Bits();
60 }
61
62
InsertRepresentationChangesForValue(HValue * value)63 void HRepresentationChangesPhase::InsertRepresentationChangesForValue(
64 HValue* value) {
65 Representation r = value->representation();
66 if (r.IsNone()) return;
67 if (value->HasNoUses()) {
68 if (value->IsForceRepresentation()) value->DeleteAndReplaceWith(NULL);
69 return;
70 }
71
72 for (HUseIterator it(value->uses()); !it.Done(); it.Advance()) {
73 HValue* use_value = it.value();
74 int use_index = it.index();
75 Representation req = use_value->RequiredInputRepresentation(use_index);
76 if (req.IsNone() || req.Equals(r)) continue;
77
78 // If this is an HForceRepresentation instruction, and an HChange has been
79 // inserted above it, examine the input representation of the HChange. If
80 // that's int32, and this HForceRepresentation use is int32, and int32 to
81 // smi changes can't cause deoptimisation, set the input of the use to the
82 // input of the HChange.
83 if (value->IsForceRepresentation()) {
84 HValue* input = HForceRepresentation::cast(value)->value();
85 if (input->IsChange()) {
86 HChange* change = HChange::cast(input);
87 if (change->from().Equals(req) && IsNonDeoptingIntToSmiChange(change)) {
88 use_value->SetOperandAt(use_index, change->value());
89 continue;
90 }
91 }
92 }
93 InsertRepresentationChangeForUse(value, use_value, use_index, req);
94 }
95 if (value->HasNoUses()) {
96 DCHECK(value->IsConstant() || value->IsForceRepresentation());
97 value->DeleteAndReplaceWith(NULL);
98 } else {
99 // The only purpose of a HForceRepresentation is to represent the value
100 // after the (possible) HChange instruction. We make it disappear.
101 if (value->IsForceRepresentation()) {
102 value->DeleteAndReplaceWith(HForceRepresentation::cast(value)->value());
103 }
104 }
105 }
106
107
Run()108 void HRepresentationChangesPhase::Run() {
109 // Compute truncation flag for phis: Initially assume that all
110 // int32-phis allow truncation and iteratively remove the ones that
111 // are used in an operation that does not allow a truncating
112 // conversion.
113 ZoneList<HPhi*> int_worklist(8, zone());
114 ZoneList<HPhi*> smi_worklist(8, zone());
115
116 const ZoneList<HPhi*>* phi_list(graph()->phi_list());
117 for (int i = 0; i < phi_list->length(); i++) {
118 HPhi* phi = phi_list->at(i);
119 if (phi->representation().IsInteger32()) {
120 phi->SetFlag(HValue::kTruncatingToInt32);
121 } else if (phi->representation().IsSmi()) {
122 phi->SetFlag(HValue::kTruncatingToSmi);
123 phi->SetFlag(HValue::kTruncatingToInt32);
124 }
125 }
126
127 for (int i = 0; i < phi_list->length(); i++) {
128 HPhi* phi = phi_list->at(i);
129 HValue* value = NULL;
130 if (phi->representation().IsSmiOrInteger32() &&
131 !phi->CheckUsesForFlag(HValue::kTruncatingToInt32, &value)) {
132 int_worklist.Add(phi, zone());
133 phi->ClearFlag(HValue::kTruncatingToInt32);
134 if (FLAG_trace_representation) {
135 PrintF("#%d Phi is not truncating Int32 because of #%d %s\n",
136 phi->id(), value->id(), value->Mnemonic());
137 }
138 }
139
140 if (phi->representation().IsSmi() &&
141 !phi->CheckUsesForFlag(HValue::kTruncatingToSmi, &value)) {
142 smi_worklist.Add(phi, zone());
143 phi->ClearFlag(HValue::kTruncatingToSmi);
144 if (FLAG_trace_representation) {
145 PrintF("#%d Phi is not truncating Smi because of #%d %s\n",
146 phi->id(), value->id(), value->Mnemonic());
147 }
148 }
149 }
150
151 while (!int_worklist.is_empty()) {
152 HPhi* current = int_worklist.RemoveLast();
153 for (int i = 0; i < current->OperandCount(); ++i) {
154 HValue* input = current->OperandAt(i);
155 if (input->IsPhi() &&
156 input->representation().IsSmiOrInteger32() &&
157 input->CheckFlag(HValue::kTruncatingToInt32)) {
158 if (FLAG_trace_representation) {
159 PrintF("#%d Phi is not truncating Int32 because of #%d %s\n",
160 input->id(), current->id(), current->Mnemonic());
161 }
162 input->ClearFlag(HValue::kTruncatingToInt32);
163 int_worklist.Add(HPhi::cast(input), zone());
164 }
165 }
166 }
167
168 while (!smi_worklist.is_empty()) {
169 HPhi* current = smi_worklist.RemoveLast();
170 for (int i = 0; i < current->OperandCount(); ++i) {
171 HValue* input = current->OperandAt(i);
172 if (input->IsPhi() &&
173 input->representation().IsSmi() &&
174 input->CheckFlag(HValue::kTruncatingToSmi)) {
175 if (FLAG_trace_representation) {
176 PrintF("#%d Phi is not truncating Smi because of #%d %s\n",
177 input->id(), current->id(), current->Mnemonic());
178 }
179 input->ClearFlag(HValue::kTruncatingToSmi);
180 smi_worklist.Add(HPhi::cast(input), zone());
181 }
182 }
183 }
184
185 const ZoneList<HBasicBlock*>* blocks(graph()->blocks());
186 for (int i = 0; i < blocks->length(); ++i) {
187 // Process phi instructions first.
188 const HBasicBlock* block(blocks->at(i));
189 const ZoneList<HPhi*>* phis = block->phis();
190 for (int j = 0; j < phis->length(); j++) {
191 InsertRepresentationChangesForValue(phis->at(j));
192 }
193
194 // Process normal instructions.
195 for (HInstruction* current = block->first(); current != NULL; ) {
196 HInstruction* next = current->next();
197 InsertRepresentationChangesForValue(current);
198 current = next;
199 }
200 }
201 }
202
203 } } // namespace v8::internal
204